Grinding machine with electric discharge machining mechanism for reshaping crush roll



Aug. 20, 1968 RYE 3,398,253

GRINDING MACHINE WITH ELECTRIC DISCHARGE MACHINING MECHANISM FOR RESHAPING CRUSH ROLL Filed Oct. 19, 1965 2 Sheets-Sheet 1 INVENTOR.

JOHN K. RYE

BY 25041. M, m

ATTORNEYS Aug. 20, 1968 J. K. RYE 3,398,253

GRINDING MACHINE WITH ELECTRIC DISCHARGE MACHINING MECHANISM FOR RESHAPING CRUSH ROLL Filed Oct. 19. 1965 2 Sheets-Sheet 2 FIG. 5

\ Jon-m K. Wa

ATTORNEYS United States Patent m GRINDING MACHINE WITH ELECTRIC DIS- CHARGE MACHINING MECHANISM FOR RESHAPING CRUSH ROLL John K. Rye, Beverly Hills, Mich., assignor to F. Jos. Lamb Company, Inc., Warren, Mich., a corporation of Michigan Filed Oct. 19, 1965, Ser. No. 497,879 7 Claims. (Cl. 219-69) ABSTRACT OF THE DISCLOSURE A grinding machine having a wheel dressing mechanism in the form of a crush roll formed of hard material such as a metal carbide and an electrode wheel for imparting the desired profile to the crush roll by means of electric discharge machining. The crush roll can be rocked from an operative position with the grinding wheel to an operative position with the electrode wheel.

This invention relates generally to grinders and more particularly to a method and apparatus wherein a crush roll for dressing a grinding wheel may be reformed between grinding cycles by electric discharge machining.

Numerous grinding machines are equipped with a crush roll mechanism for dressing the grinding wheel periodically between grinding operations. Eventually the crush roll wears to a point where its contour must be reformed. This normally necessitates removal of the crush roll from the grinding machine and reforming its shape on another machine such as by a diamond wheel or the like. This procedure is not only time consuming but also necessitates shutting down the grinding machine.

It is an object of this invention to eliminate the necessity of removing the crush roll from the grinding machine for the purpose of reforming the contour thereof.

A further object of the invention resides in the provision of a method and apparatus for reforming the contour of a crush roll without interrupting the operation of the grinding machine on which it is mounted.

Other objects, features and advantages of the invention will become evident from the [following description, considered with the accompanying drawings, in which:

FIG. 1 is a side view, partly schematic, of apparatus according to the invention and shows an abrasive wheel crush roll in a retracted position where it may be reformed in the apparatus.

FIG. 2 is a side view similar to FIG. 1 showing the crush roll advanced into contact with a grinding wheel in order to dress it.

FIG. 3 is a detail section taken on line 3-3 of FIG.5 showing the profile of an electrode wheel which serves as a reforming tool in the apparatus.

FIG. 4 is a fragmentary plan view of the apparatus of FIG. 2.

FIG. 5 is a longitudinal section taken on line 5-5 of FIG. 4 showing the internal construction of the apparatus.

The method aspect of invention is carried out by grinding a workpiece with an abrasive wheel, dressing the abrasive wheel with a crush roll and reforming the crush roll by electric discharge machining. The crush roll is made of a very hard material, such as a metal carbide or the like, which is harder than the material of the abrasive grinding wheel. Despite its hardness, the crush roll may be formed accurately to the proper surface profile by electric discharge machining.

One embodiment of apparatus according to the invention includes a movable member which supports the Patented Aug. 20, 1968 crush roll between the abrasive wheel and an electrode wheel having a reforming surface of the desired profile. By operation of a driving mechanism, the movable member advances the crush roll into contact with the abrasive grinding wheel to true it up for a grinding operation, and retracts the crush roll to a position adjacent the electrode wheel where the roll is reformed by electric discharge machining.

The grinding machine 10 has an abrasive grinding wheel 12 supported for rotation on a spindle 14 which is rotated by an electric motor (not shown) to grind a workpiece 16. The surface of abrasive wheel 12 ordinarily deteriorates due to the abrasion of grinding. In order to dress abrasive wheel 12 so that its contour will conform exactly to that required, a crush roll 18 is provided in the apparatus. Roll 18 on at least its outer surface may be of metal carbide or the like, as previously mentioned, which makes it sufiiciently hard that it does not wear very much from one dressing operation to another. Some wear of the dressing surface occurs, however, so an electrode wheel 20 having a reforming surface is also provided in the appartus. Electrode wheel 20 is supported for rotation on a spindle 22 which is journalled in upright arms 24 on a supporting base 26. Crush roll 18 is supported for rotation on spindle 2'8 journalled in a frame 30 which is pivotally supported on base 26 by a pin 32. Frame 30 comprises a pair of axially spaced levers having angularly related arms 31 and 33, the levers being interconnected to form the integral frame 30 by cross arms 35 and 37 (FIGS. 4 and 5). Cross arm 37 is connected to a jack mechanism 39.

Crush roll 18 is located betwen abrasive wheel 12 and electrode wheel 20 such that it may be rocked back and forth between the two wheels about pivot pin 32. When it is desired to dress abrasive wheel 12, frame 30 is moved pivotally counterclockwise by operation of jack mechanism 39 to place dressing roll 18 in contact with abrasive wheel 12 (FIG. 2). When the dressing operation is completed, frame 30 may be pivoted clockwise by lowering jack mechanism 39 to retract or disengage crush roll 18 and move it to a position adjacent electrode wheel 20 (FIG. 1) wheren the surface of crush roll 18 is close to but spaced [from the reforming surface of electrode wheel 20.

Durin reforming, crush roll 18 is rotated slowly counterclockwise by an electric motor 34 mounted on one arm 33 of frame 30 (FIG. 4). Motor 34 is operatively connected by a worm wheel drive 36 to spindle 28 for rotating the spindle. Electrode wheel 20 is also rotated during reforming but at a faster speed than crush roll 18. The power for rotating electrode wheel 20 is supplied by a high speed electric motor 38 (FIG. 5) connected by a worm drive 40 to spindle 22. The motor which rotates abrasive wheel 12 is also a high speed type and it rotates wheel 12 faster than roll 18 is rotated. Wheel 20 may be made of carbon, and electrical contact is made to this wheel by means of brushes (not shown) (FIG. 5). Crush roll 18 is ordinarily maintained at ground potential and a high potential either A.C. or interrupted DC. is applied to electrode wheel 20 from a power source (not shown). It will be understood, however, that high potential could alternatively be applied to crush roll 18 while maintaining electrode wheel 20 at a reference potential. The objective is to produce an electric field between the dressing surface of roll 18 and the reforming surface of electrode wheel 20 which causes intermittent arcing as crush roll 18 rotates. The arcing removes material from the dressing surface of roll 18. By this electric discharge process, the dressing surface of roll 18 is made to conform inversely with the reforming surface of electrode wheel 20.

The surface profiles of wheels 12 and 20 and crush roll 18 will vary from job to job. An illustrative profile for electrode wheel 20 is shown in FIGS. 3 and 4. There is a V-groove 52 between two land areas 54 and 56 and flat recesses 58 and 60 on opposite sides of another land 62. The surface profile of abrasive wheel 12 is identical to that of electrode wheel 20, whereas the surface profile of crush roll 18 inversely matches that of the electrode wheel, as is evident in FIG. 4.

A dielectric oil flows from the outlet 64 of a liquid supply system into the space between the adjacently -positioned dressing surface of crush roll 18 and reforming surface of wheel 20 (FIG. 1). The oil is desirable for its dielectric properties and also as a medium for carrying the metal particles away from roll 20 during reforming. A trough 66 (FIG. is supported on base 26 beneath electrode wheel to collect the oil and has a drain outlet 68 at its bottom end 70 which connects with a pump and filter (not shown).

The jack mechanism 72 for shifting frame includes a worm screw 74 threaded through a tapped opening in a nut 76 having pins 77 journalled for rotation in lugs 81 and 83 which are integral with cross arm 37 of the frame. Worm screw 74 may be rotated in either rotary direction by a reversible electric motor 78. The worm screw and motor are pivotally supported on base 26 by pivot pin 79. In one direction of rotation, worm screw 74 raises arms 33, and 37 of frame 31 and thereby pivots the frame about pin 32 to move dressing roll 18 into contact with abrasive grinding wheel 12. Conversely, when worm screw 74 rotates in the opposite direction, it lowers arms 33 and 37 to retract dressing roll 18 to its reforming position adjacent electrode wheel 20.

Motor 78 is preferably of the type that can be rotated rapidly to produce a rapid advance and rapid retraction or slowly to produce a slow feed rate when the crush roll is in operative relation with abrasive wheel 12 on electrode wheel 20. Motor 34, which rotates crush roll 18, is likewise a variable speed motor which is adapted to rotate crush roll 18 rapidly when in operative relation with abrasive wheel 12 and very slowly when in operative relation with electrode wheel 20. Motor 34 is preferably of the type that can be rotated by very small increments under the control of the potential of the are established between roll 18 and wheel 20 to control the rate of stock removal by the electrical discharge action.

Electrode wheel 20 is dressed between successive operations on crush roll 18 by means of a wheel dresser in the form of a blade 80, the edge of which is ground with a contour coresponding to that required on the workpiece to be ground. Dresser 80 is mounted in a guideway 82 within a housing 83 on base 26 for movement radially toward and away from the periphery of electrode wheel 20. Dresser 80 is shifted -in guideway 80 by a screw 84 engaging a threaded lug 86 on the dresser. Screw 84 is rotated in opposite directions by a Worm drive 88 from a motor or manual turning knob 90.

In accordance with the invention, reforming of a crush roll may be accomplished without removing the crush roll from the grinding machine. Reforming may take place during or between grinding cycles such that there is no disturbance of the grinding schedule. The invention may be applied to many types of grinders and is not limited in its utility to the specific grinding machine described and illustrated herein by way of example.

I claim:

1. In a grinding machine the combination comprising an abrasive wheel supported for rotation to grind a workpiece, a rotatably-supported crush roll for dressing the abrasive wheel, a rotatably-supported electrode wheel, means movably supporting the crush roll between the abrasive wheel and the electrode wheel, a feed screw operatively connected to said movable means, a reversible motor operatively connected with the feed screw for rotating the same in opposite directions for shifting the crush roll in one direction into contact with the abrasive wheel and in the opposite direction to a position adjacent the electrode wheel, said electrode wheel having a surface adapted to reform the dressing surface of the crush roll by electric discharge machining, liquid supply means having an outlet adjacent the electrode wheel for supplying a dielectric liquid to the space between adjacent portions of the crush roll and the electrode wheeel when they are adjacently positioned, a motor for rotating the electrode wheel at a relatively high speed, a motor for rotating the crush roll at a speed substantially lower than the speed of the electrode wheel and electrical energy supplying means connecting said crush roll and said electrode wheel in circuit for electric discharge machining.

2. In a grinding machine the combination comprising a support, an abrasive wheel journalled on said support for grinding a workpiece, a crush roll journalled on said support, an electrode wheel journalled on said support, said crush roll being relatively movable toward and away from the abrasive wheel and electrode wheel so that the abrasive wheel and crush roll can be brought into tangential rolling contact and the crush roll and electrode wheel can be brought into close tangential relation, said crush roll comprising an electrically conductive metal of the type which is too hard to be shaped by conven tional metal cutting tools, said electrode wheel having a surface adapted to reform the dressing surface of the crush roll by electric discharge machining, power means for rotating said crush roll and said abrasive and electrode wheels and electrical energy supplying means connecting said crush roll and said electrode wheel in circuit for electric discharge machining.

3. The combination called for in claim 2 wherein the dressing surface of said crush roll comprises a metal carbide.

4. The combination called for in claim 2 including a blade type wheel dresser for said electrode wheel, said wheel dresser being mounted on said support for relative movement toward and away from the periphery of the electrode wheel.

5. The combination called for in claim 2 wherein said crush roll and said wheels are arranged with their axes generally parallel, means movably mounting said crush roll on said support for movement in opposite directions toward and away from said abrasive wheel and said electrode wheel, a feed screw operatively connected with said last-mentioned means for moving the same and a reversible motor operatively connected with said feed screw.

6. The combination called for in claim 2 wherein said crush roll and said wheels are arranged with their axes generally parallel, a rocking lever pivotally mounted on said support, said crush roll being journalled on said rocking lever and being disposed between said abrasive wheel and said electrode wheel for pivotal movement with said lever toward and away from the abrasive wheel and the electrode wheel and means for rocking said lever in opposite directions including a reversible motor operatively connected with said lever.

7. The combination called for in claim 6 wherein said lever rocking means includes a nut on said lever and a feed screw engaged with said nut, said feed screw being operatrvely connected with said motor for rotation in opposite directions.

References Cited UNITED STATES PATENTS 2,456,762 12/ 1948 Wilson -11.2 2,720,062 10/1955 Fouquet 125-11.2 X 3,061,708 10/1962 Pfau 219-69 3,205,335 9/1965 Johnston et al 219-69 3,222,494 12/ 1965 OConnor 219-69 RICHARD M. WOOD, Primary Examiner.

R. F. STAUBLY, Assistant Examiner. 

